If each click costs more than the margin earned per conversion, the funnel loses money, so the break-even rate becomes the key signal. Tracking click-throughs, landing page conversions, and repeat purchases helps reveal where profitability starts. For some campaigns, even 1–2% conversion can work if commissions are high; for others, you might need 5–10% to stay in the green. Watching cohort performance and cost per acquisition shows whether scaling is safe or just burning budget.